In modern textile machines, a plurality of weft feeders are slave to a master managing unit, from which they receive individual control signal or programming signals for individual parameter, and to which they transmit information signals concerning the state of the machine or process variables. This bidirectional conversation has typically taken place via a star connection between the managing unit and the individual weft feeders, and the connection, as a rule, has used differential-type buses, say according to standards RS485 or CAN.
As the number of slave weft feeders increases (which number in large machines may reach and exceed a hundred), the number of cables in the star connection increases proportionally, thereby also increasing the bulk of the cable bundles and making it difficult to neatly arrange them. This situation not only imparts an unpleasant look to the machines, but also may hinder the operation of the personnel.
Moreover, with the above arrangement the cables will have variable lengths, depending on the distance of the weft feeder from the master unit cabinet, and the manufacturer of the weft feeders will therefore have to stock a wide range of cable lengths.
Further, as persons skilled in the art will appreciate, a long cable may create problems due to the reflections of the signal traveling on the bus, and this circumstances places serious limits to the bandwidth, i.e. to the signal transmission speed along the bus.
Another and even more serious drawback of the star-connected bus distribution on machines having a large number of weft feeders concerns the addressing of the receivers of the respective weft feeders. In the conventional arrangement for addressing the receivers (which are permanently connected to the bus) the electronic card of each weft feeder houses an electric resistance whose value is unique for that receiver; the resistance is measured and compared with the address associated to the signal received via the bus. However, the analog character of this approach is only suitable for addressing half a score weft feeders.